Investigative clinical therapeutic studies and clinical therapeutic studies in children with acute leukemia, malignant lymphoma, histiocytosis X, and malignant solid tumors (brain tumors, neuroblastoma, Wilms' tumor, osteogenic sarcoma, Ewing's sarcoma, soft tissue sarcoma and miscellaneous malignant neoplasms) are conducted in four areas: 1) Phase I coordinated studies of human pharmacologic and toxicologic aspects of new anticancer agents and new combinations in dosage regimens; 2) Phase Ii systematic investigations of the effectiveness of individual anticancer agents or treatment programs in specific tumors; 3) Phase Ii comparative evaluations of selected drugs and/or therapy regimens; and 4) Specific laboratory investigations in immunology and clinical pharmacology. The functioning cooperative group study mechanism is utilized to increase the size of the study population and to shorten the duration of study. Members of the project professional personnel participate in the cooperative group study mechanism as study coordinators, intergroup study direction, and scientific program guidance. Independent investigative probes are undertaken to explore leads resulting from or directed towards group studies. Several intergroup and national studies, ongoing and projected (National Wilms' Tumor Study, Intergroup Rhabdomyosarcoma Study, Intergroup Ewing's Sarcoma Study, Hepatoma Study and Hodgkin's Disease Study) are included. This research will be executed in an integrated multimodal manner. Attention to centralized data management will be given for the individual specialties of pediatrics, surgery, radiotherapy, pathology, and laboratory support. Special attention will be given to clinical pharmacology and immunological investigation required for optimal execution of current protocols and protocols to come employing high dose methotrexate, cis-platinum, or protocols requiring classification of lymphoid malignancies, in order to establish proper therapy assignment.